Claire and Haley, two 13-year-old best friends, embark on the adventure of their lives when they discover a mermaid named Aquamarine in a swimming pool. Claire and Hailey are trying to come to terms with Hailey's impending departure: She's moving to Australia with her marine biologist mother after this last weekend of the summer. The beautiful, blue-haired, 18-year-old mermaid swam away from home just before her arranged marriage, in search of real love. If she can prove to her father that love is not a myth, he'll let her out of the underwater wedding, but he's only giving her three days. Aqua enlists the help of Claire and Haley, who are self-styled relationship experts. Aqua promises to grant Claire and Hailey the wish of their choice if they help her and the girls jump at the opportunity–because unless something magical happens, Hailey will be moving.